Giant cell arteritis (GCA), also known as temporal arteritis, is a disease that usually only occurs in older adults. GCA causes inflammation of blood vessels, or vasculitis. In order to properly treat this disease, it is critical that the level of disease activity can be determined over the course of the disease. The purpose of this study is to determine new biological markers, or biomarkers, that may be used to assess the severity of disease in people with GCA.